You're not officially supposed to listen to Christmas music until after Thanksgiving, but Pentatonix's a cappella cover of "Little Drummer Boy" is worth breaking the rules for.

The five-person singing group — comprised of Avi Kaplan, Scott Hoying, Kirstin Maldonado, Kevin Olusola and Mitch Grassi — formed to compete in the NBC a cappella competition show "The Sing Off." The group released its "PTXmas" album just in time for the holidays.